A phase I trial of genetically modified Salmonella typhimurium expressing cytosine deaminase (TAPET-CD, VNP20029) administered by intratumoral injection in combination with 5-fluorocytosine for patients with advanced or metastatic cancer. Protocol no: CL-017. Version: April 9, 2001

An attenuated strain of Salmonella typhimurium, designated VNP20009, was generated by deletion of the msbB and purl genes. When VNP20009 was administered intravenously (IV) to mice bearing spontaneous, syngeneic, or human xenograft tumors, the bacteria accumulated preferentially within the extracellular components of tumors, forming tumor-to-normal tissue ratios exceeding 300-1000 to 1. NVP20009 was administered safely at doses up to 2.5 x 10(9) cfu/kg in monkey toxicology studies. Based on the preclinical data, VNP20009 entered Phase I human clinical trials in November 1999, and has now been administered to >45 patients by IV or direct intratumoral injection. By the intratumoral route, a maximum tolerated dose has not been reached, and dose escalation continues past the current dose level of 4 x 10(7)/m2. Furthermore, VNP20009 persisted in injected tumors for at least 2 weeks in 8/11 patients treated to date. By 30-min IV administration, a maximum tolerated dose (MTD) of 3 X 10(8) cfu/m2 has been established. In all patients treated to date, VNP20009 was not shed in urine or stool. VNP20009 has been further modified by chromosomal insertion of an E. coli cytosine deaminase (CD) gene at the deltamsbB locus which, when expressed, converts 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU). The CD containing VNP20009 was designated TAPET-CD or VNP20029. TAPET-CD had similar efficacy and safety in murine tumor models and similar safety profiles in animal toxicology studies, compared to its parent VNP20009. Specifically, TAPET-CD had a reduced virulence of >10,000 fold, when compared to the wild-type Salmonella strain. It was well-tolerated at doses up to 2 x 10(6) cfu/mouse and 1 X 10(10) cfu/monkey. After an IV or direct tumor injection to tumor-bearing mice, TAPET-CD reached tumor levels as high as 10(8)-10(9) cfu/gm. When compared to the accumulation in liver or spleen, the normal tissues with the greatest colonization of TAPET-CD, tumor-to-normal tissue ratios of TAPET-CD were 300-1000 to 1. TAPET-CD also caused tumor growth inhibition of >90% in several murine tumor models. When 5-FC was administered by intraperitoneal (IP) injection once or 3 times daily to tumor-bearing mice that had been pre-treated with TAPET-CD, high levels of 5-FU (reaching 20-40 microM/g) were detected in the tumor, with low or undetectable 5-FU levels in normal tissues (e.g., spleen, liver, etc.). Furthermore, co-administration of 5-FC and TAPET-CD in 4 different murine tumor models enhanced anti-tumor activity compared to the significant anti-tumor activity of TAPET-CD alone, further confirming the benefit of the inserted CD gene. On the basis of the preclinical data, a Phase I clinical protocol is proposed in which advanced cancer patients will receive TAPET-CD by direct intratumoral injection and 5-FC. TAPET-CD will be administered on day 1. 5-FC will be given orally q8h daily beginning day 4 or when all toxicities of TAPET-CD have resolved to < or = grade 1, and continued for 14 days. Tumor tissues will be sampled to verify TAPET-CD colonization and to measure intratumoral 5-FC and 5-FU concentrations on day 8. A second sample of tumor tissue will be obtained between day 15-17 in selected patients to confirm the persistence of high levels of bacteria in tumor and to obtain a second measurement of 5-FC and 5-FU intra-tumoral concentrations. The TAPET-CD/5-FC treatment cycle will be repeated in appropriate patients on day 29.     

Experimental gene therapy for brain tumors using adenovirus-mediated transfer of cytosine deaminase gene and uracil phosphoribosyltransferase gene with 5-fluorocytosine

Transduction of the cytosine deaminase (CD) gene into tumor cells followed by administration of 5-fluorocytosine (5-FC), called 5-FC/CD gene therapy, was created as suicide gene therapy for various cancers. The uracil phosphoribosyltransferase (UPRT) gene, which is absent from mammalian cells, directly converts 5-fluorouracil (5-FU) to 5-fluorouridine 5'-monophosphate. We evaluated whether the coexpression of CD and UPRT genes could generate a synergistic antitumor effect on experimental brain tumors. In vitro study showed that 9L cells, transduced with the UPRT gene by an adenovirus, were 16 times more sensitive to 5-FU, and CD + UPRT-transduced cells were 6,000 times more sensitive to 5-FC than parent cells, indicating that the acquisition of CD and UPRT further increased the 5-FC sensitivity of 9L cells compared with cells transduced with CD alone. In a rat brain tumor model, decreased amounts of CD and UPRT vectors were inoculated into the tumors to detect any additional effect of UPRT. CD and UPRT coexpression followed by 5-FC administration showed an antitumor effect as detected by sequential magnetic resonance imaging. This therapy significantly prolonged animal survival. These results suggest that 5-FC/CD + UPRT gene therapy can enhance the antitumor effect of 5-FC/CD gene therapy. Consequently, this approach might be a more feasible modality for the treatment of malignant brain tumors.     

Complex interactions between the replicating oncolytic effect and the enzyme/prodrug effect of vaccinia-mediated tumor regression

Replicating viruses for cancer gene therapy have beneficial antitumor effects, however, in the setting of an enzyme/prodrug system, the interactions between these viruses and the activated agents are complex. A replicating vaccinia virus expressing the cytosine deaminase gene (VVCD), which converts the prodrug 5-FC into 5-FU, was characterized in vitro and in vivo for its antitumor effects and pathogenicity. Replicating VVCD (+/-5-FC) at various MOIs was used to infect MC38 murine colon adenocarcinoma cells. At high MOIs (>0.1) virus alone was able to kill the majority (65-90%) of cells by day 5 with no additional benefit from prodrug. At low MOIs only the effect of prodrug is seen. Cell lysates demonstrated 300-fold reduced viral recovery from cells treated with both VVCD and 5-FC compared with controls treated with virus alone. Nude mice bearing subcutaneous MC38 tumors were injected with VVCD (or control) and treated with 5FC or control. Mice injected with VVCD (with or without 5FC treatment) had smaller tumors than the controls, suggesting that replicating vaccinia alone is cytotoxic to tumors in vivo. The addition of 5-FC improved the antitumor response when a low dose of virus was injected into tumors. Also, compared with mice that received virus alone, those that received VVCD and 5FC had significantly prolonged survival from virus-mediated death. In conclusion, the addition of an enzyme/prodrug system to a replicating virus can improve the antitumor response and decrease viral pathogenicity. Gene Therapy (2000) 7, 1217-1223.     

Adipose Tissue�Cderived Mesenchymal Stem Cells Expressing Prodrug-converting Enzyme Inhibit Human Prostate Tumor Growth

The ability of human adipose tissue–derived mesenchymal stem cells (AT-MSCs), engineered to express the suicide gene cytosine deaminase::uracil phosphoribosyltransferase (CD::UPRT), to convert the relatively nontoxic 5-fluorocytosine (5-FC) into the highly toxic antitumor 5-fluorouracil (5-FU) together with their ability to track and engraft into tumors and micrometastases makes these cells an attractive tool to activate prodrugs directly within the tumor mass. In this study, we tested the feasibility and efficacy of these therapeutic cells to function as cellular vehicles of prodrug-activating enzymes in prostate cancer (PC) therapy. In in vitro migration experiments we have shown that therapeutic AT-MSCs migrated to all the prostate cell lines tested. In a pilot preclinical study, we observed that coinjections of human bone metastatic PC cells along with the transduced AT-MSCs into nude mice treated with 5-FC induced a complete tumor regression in a dose dependent manner or did not even allow the establishment of the tumor. More importantly, we also demonstrated that the therapeutic cells were effective in significantly inhibiting PC tumor growth after intravenous administration that is a key requisite for any clinical application of gene-directed enzyme prodrug therapies.     

Anticancer efficacy of systemically delivered anaerobic bacteria as gene therapy vectors targeting tumor hypoxia/necrosis

A major obstacle in cancer gene therapy is selective tumor delivery. Previous studies have suggested that genetically engineered anaerobes of the genus Clostridium might be gene therapy vectors because of their ability to proliferate selectively in the hypoxic/necrotic regions common to solid tumors. However, the tumor colonization efficiency of the strain previously used was insufficient to produce any antitumor effect. Here we describe for the first time the successful transformation of C. sporogenes, a clostridial strain with the highest reported tumor colonization efficiency, with the E. coli cytosine deaminase (CD) gene and show that systemically injected spores of these bacteria express CD only in the tumor. This enzyme can convert the nontoxic prodrug 5-fluorocytosine (5-FC) to the anticancer drug 5-fluorouracil (5-FU). Furthermore, systemic delivery of 5-FC into mice previously injected with CD-transformed spores of C. sporogenes produced greater antitumor effect than maximally tolerated doses of 5-FU. Since most human solid tumors have hypoxic and necrotic areas this vector system has considerable promise for tumor-selective gene therapy.     

Fractionated radiation therapy in combination with adenoviral delivery of the cytosine deaminase gene and 5-fluorocytosine enhances cytotoxic and antitumor effects in human colorectal and cholangiocarcinoma models

Radiosensitization of human gastrointestinal tumors by 5-fluorouracil (5-FU) has been studied in vitro and clinically in human cancer therapy trials. The bacterial enzyme cytosine deaminase (CD) converts the nontoxic prodrug 5-fluorocytosine (5-FC) into 5-FU. Human colon cancer cells stably expressing CD have been shown by other investigators to be sensitized to radiation following treatment with 5-FC. We previously used an adenoviral vector under control of the cytomegalovirus promoter (AdCMVCD) encoding the CD gene in combination with 5-FC and a single fraction of radiation exposure to enhance cytotoxicity to human cholangiocarcinoma cells in vitro and in vivo. The purpose of this study was to determine whether AdCMVCD infection and 5-FC with multiple fraction low-dose radiotherapy results in enhanced cytotoxicity. In the present study, we utilized AdCMVCD and 5-FC with single fraction radiotherapy to demonstrate enhanced cytotoxicity to WiDr human colon carcinoma cells in vitro. Additionally, we tested this gene therapy/prodrug treatment strategy employing a fractionated radiation dosing schema in animal models of WiDr colon carcinoma and SK-ChA-1 cholangiocarcinoma. A prolonged WiDr tumor regrowth delay was obtained with AdCMVCD infection in combination with systemic delivery of 5-FC and fractionated external beam radiation therapy compared with control animals treated without radiation, without 5-FC, or without AdCMVCD. The results of treatment with AdCMVCD + 5-FC + radiation therapy to cholangiocarcinoma xenografts were equivalent to those obtained with systemic 5-FU administration + radiation. Thus, the use of AdCMVCD can be effectively combined with clinically relevant 5-FC and radiation administration schemes to achieve enhanced tumor cell killing and increased control of established tumors of human gastrointestinal malignancies.     

Dual targeting of tumor angiogenesis and chemotherapy by endostatin-cytosine deaminase-uracil phosphoribosyltransferase

Several antiangiogenic drugs targeting VEGF/VEGF receptor (VEGFR) that were approved by the Food and Drug Administration for many cancer types, including colorectal and lung cancer, can effectively reduce tumor growth. However, targeting the VEGF signaling pathway will probably influence the normal function of endothelial cells in maintaining homeostasis and can cause unwanted adverse effects. Indeed, emerging experimental evidence suggests that VEGF-targeting therapy induced less tumor cell-specific cytotoxicity, allowing residual cells to become more resistant and eventually develop a more malignant phenotype. We report an antitumor therapeutic EndoCD fusion protein developed by linking endostatin (Endo) to cytosine deaminase and uracil phosphoribosyltransferase (CD). Specifically, Endo possesses tumor antiangiogenesis activity that targets tumor endothelial cells, followed by CD, which converts the nontoxic prodrug 5-fluorocytosine (5-FC) to the cytotoxic antitumor drug 5-fluorouracil (5-FU) in the local tumor area. Moreover, selective targeting of tumor sites allows an increasing local intratumoral concentration of 5-FU, thus providing high levels of cytotoxic activity. We showed that treatment with EndoCD plus 5-FC, compared with bevacizumab plus 5-FU treatment, significantly increased the 5-FU concentration around tumor sites and suppressed tumor growth and metastasis in human breast and colorectal orthotropic animal models. In addition, in contrast to treatment with bevacizumab/5-FU, EndoCD/5-FC did not induce cardiotoxicity leading to heart failure in mice after long-term treatment. Our results showed that, compared with currently used antiangiogenic drugs, EndoCD possesses potent anticancer activity with virtually no toxic effects and does not increase tumor invasion or metastasis. Together, these findings suggest that EndoCD/5-FC could become an alternative option for future antiangiogenesis therapy.     

Sensitization to Low Dose 5-Fluorouracil: SUBSEQUENT ENHANCEMENT OF ITS SYSTEMIC ANTITUMOR EFFECT IN THE RAT

This report describes a novel method of immunochemotherapy; the active immunization to the drug 5-fluorouracil (5-FU) with enhanced antitumor activity resulting from its subsequent systemic administration. Two metastasizing carcinomas in the Fischer strain (F344) rat have been used: a chemically induced bladder carcinoma (FBCa) and a spontaneous mammary adenocarcinoma (MACa). Both tumors grow rapidly and result in 100% mortality within 10 wk of implantation. Neither tumor is sensitive to systemic 5-FU alone. Intradermal sensitization to 5-FU before FBCa tumor implantation, followed by 5-FU administered systemically, resulted in significant tumor regression and improvement in survival with eradication of all tumor and cure in 20% of animals. A similar antitumor effect was observed with the MACa. A comparable drug effect was observed when methotrexate sensitization was given before FBCa implantation followed by systemic MTX. Specificity to the sensitizing drug was demonstrated by the lack of effect of sensitization with either 5-FU or MTX unless followed by systemic therapy with the requisite sensitizing agent. Sensitization to 5-FU has also been assessed after FBCa implantation followed by resection of the local tumor. Resection was performed after distant tumor metastases had occurred, and was followed by systemic 5-FU therapy. Whereas tumor resection alone failed to cure any animal, sensitization to 5-FU increased cure rate fourfold over animals receiving systemic 5-FU alone. Antibody to 5-FU in the sera of sensitized animals has been suggested by an immunoenzymatic staining technique and its specificity confirmed in a radioimmunoassay. It is postulated that a combination of the systemic agent and the antibody elicited to it by sensitization produces the significant antitumor effect observed. The antitumor effect observed with this new approach to immunochemotherapy warrants further experimental and clinical study.     

In vivo gene therapy for colon cancer using adenovirus-mediated, transfer of the fusion gene cytosine deaminase and uracil phosphoribosyltransferase.

Virus-directed enzyme prodrug therapy (VDEPT) utilising cytosine deaminase (CD) converts 5-fluorocytosine (5-FC) into the chemotherapy agent, 5-fluorouracil (5-FU), and has entered into a clinical trial for metastatic colon cancer. To improve this system, a replication-deficient adenovirus, containing a bifunctional fusion gene, CD:uracil phosphoribosyltransferase (UPRT), was constructed (AdCDUPRT). UPRT enhances the conversion of 5-FU into its active metabolites, which inhibit DNA and RNA synthesis. In vitro, AdCDUPRT infection of colon cancer cells resulted in a marked increase in sensitisation to 5-FU, compared with AdCD-infected or uninfected cells. The corollary is a approximately 100-fold and approximately 10 000-fold increase in sensitisation to 5-FC in AdCDUPRT-infected cells, compared to AdCD-infected and uninfected cells, respectively. There was a strong bystander effect in vitro, 70% of tumour cells were killed by 5-FC when only 10% of cells expressed CDUPRT. In vivo, athymic mice with colon cancer xenografts treated with intratumoral AdCDUPRT and intraperitoneal 5-FC, significantly reduced tumour growth rates compared with untreated controls (P = 0.02), whereas AdCD/5-FC treated mice did not. At higher AdCDUPRT virus doses, 5-FC and 5-FU were equally effective at delaying tumour growth compared with controls. In summary, VDEPT for colon cancer utilising AdCDUPRT is more effective than AdCD and the bifunctional CDUPRT gene enables the use of either 5-FC or 5-FU as prodrugs.     

Efficacy of a nitric oxide-releasing nonsteroidal anti-inflammatory drug and cytotoxic drugs in human colon cancer cell lines in vitro and xenografts

We previously showed that NCX 4040 inhibits in vitro and in vivo tumor growth and induces apoptosis in human colon cancer cell lines. On the basis of these results, NCX 4040 antitumor activity in combination with 5-fluorouracil (5-FU) or oxaliplatin was evaluated in vitro and in vivo in human colon cancer models. The cytotoxicity of different NCX 4040 and 5-FU or oxaliplatin combination schemes was evaluated on a panel of colon cancer lines (LoVo, LoVo Dx, WiDr, and LRWZ) by the sulforhodamine B assay, and apoptosis was assessed by flow cytometry. NCX 4040 and 5-FU combination was always additive in vitro regardless of the scheme used. Sequential NCX 4040-->oxaliplatin treatment produced a strong synergism in three cell lines, with a ratio index ranging from 3.7 to 4. The synergistic effect was accompanied by apoptosis induction (up to 40%). In the in vivo experiments, xenografted mice were treated with the sequential combination of NCX 4040 and oxaliplatin, and apoptosis was evaluated immunohistochemically in excised tumors. Furthermore, in WiDr xenografts, this sequence caused a significantly higher reduction ( approximately 60%) in tumor growth compared with single-drug treatments and produced extensive apoptotic cell death (15.3%), significantly higher (P < 0.01) than that observed in untreated tumors (2.7%) or in tumors treated with NCX 4040 (5.1%) or oxaliplatin (5.7%) alone. These data show that NCX 4040 sensitizes colon cancer cell lines to the effect of antitumor drugs and suggests that their combination could be useful for the clinical management of colon cancer.     

5-fluorocytosine-related bone-marrow depression and conversion to fluorouracil: a pilot study

The aim of this study is to investigate whether fluorouracil (5-FU) could be responsible for bone-marrow depression occurring in fluorocytosine (5-FC) treated patients. Six 5-FC treated patients were included in this pilot study. Toxicity was monitored by means of thrombocyte and leucocyte counts. 5-FC and 5-FU serum levels were measured using a high-performance liquid chromatography (HPLC) assay that allows simultaneous determination of both compounds. The amounts of 5-FU in the 34 available serum samples remained below the limit of quantitation (< 0.05 mg/L), whereas 5-FC levels could be detected in all samples. Instead, low levels of the 5-FU catabolite alpha-fluoro-beta-alanine (FBAL) were detected in several of the investigated serum samples. In case of three patients thrombocyte counts remained within the normal range during 5-FC treatment, whereas one patient developed thrombocytopenia (50 x 10(9) thrombocytes/L) during therapy. Furthermore, one patient developed leucocytopenia (2.6 x 10(9) leucocytes/L) during 5-FC therapy, whereas the remaining five patients were suffering from leucocytosis prior to 5-FC therapy. In conclusion, we found nondetectable 5-FU serum concentrations (< 0.05 mg/L) in ICU patients treated with intravenous 5-FC, making it unlikely that 5-FC-associated toxicity results from 5-FU exposure in patients receiving intravenous 5-FC therapy. These findings may be explained by the fact that our patients received 5-FC intravenously instead of orally, therefore not allowing active conversion of 5-FC to 5-FU by the human intestinal microflora.     

Evaluation of recombinant human tumor necrosis factor by scheduled intratumoral administration in mice bearing transplantable tumors

The antitumor effect of recombinant human tumor necrosis factor (rTNF) was examined against Meth A fibrosarcoma in BALB/c mice and Sarcoma-180 in ddY mice. Significant hemorrhagic necrosis in tumor tissues occurred within 24 hr when optimal rTNF (1,000 to 5,000 units per mouse) was injected intratumorally on day 5 after intradermal inoculation of 5 x 10(5) tumor cells. Complete tumor regression resulted when two repeated courses of administration a week, each for 3 consecutive days, were given. For this marked effect to occur, however, initial tumor weight should not be greater than 1 g. When the initial tumor was greater than 1 g the surgical removal of tumor tissues was conducted and followed by rTNF administration. This caused hemorrhagic necrosis and the regression was the case with smaller tumors. When the cured mice were rechallenged with same tumors, more than 60% of mice rejected the tumors in a specific manner. In spite of such demonstration of specific immunity, well-known immunological effector mechanisms such as augmentation of natural killer cell activity, activation of antibody dependent cellular cytotoxicity or induction of interferon activity by rTNF were not detected in normal and tumor-bearing mice, suggesting that the activation of immunoregulatory cells by TNF itself may not involve at least in an early stage of TNF treatment. These results suggest that rTNF is a potent therapeutic agent for a certain solid tumor when the protocol of administration is optimized.     

Molecular chemotherapy of pancreatic cancer using novel mutant bacterial cytosine deaminase gene

The combination of molecular chemotherapy with radiation therapy has the potential to become a powerful approach for treatment of pancreatic cancer. We have developed an adenoviral vector (AdbCD-D314A) encoding a mutant bacterial cytosine deaminase (bCD) gene, which converts the prodrug 5-fluorocytosine (5-FC) into the active drug 5-fluorouracil. The aim of this study was to investigate AdbCD-D314A/5-FC-mediated cytotoxicity in vitro and therapeutic efficacy in vivo alone and in combination with radiation against human pancreatic cancer cells and xenografts. AdbCD-D314A/5-FC-mediated cytotoxicity alone and in combination with radiation was analyzed using crystal violet inclusion and clonogenic survival assays. CD enzyme activity was determined by measuring conversion of [(3)H]5-FC to [(3)H]5-fluorouracil after adenoviral infection of pancreatic cancer cells in vitro and pancreatic tumor xenografts by TLC. S.c. pancreatic tumor xenografts were used to evaluate the therapeutic efficacy of AdbCD-D314A/5-FC molecular chemotherapy in combination with radiation therapy. AdbCD-D314A infection resulted in increased 5-FC-mediated pancreatic cancer cell killing that correlated with significantly enhanced CD enzyme activity compared with AdbCDwt encoding wild-type of bCD. Animal studies showed significant inhibition of growth of human pancreatic tumors treated with AdbCD-D314A/5-FC in comparison with AdbCDwt/5-FC. Also, a significantly greater inhibition of growth of Panc2.03 and MIA PaCA-2 tumor xenografts was produced by the combination of AdbCD-D314A/5-FC with radiation compared with either agent alone. The results indicate that the combination of AdbCD-D314A/5-FC molecular chemotherapy with radiation therapy significantly enhanced cytotoxicity of pancreatic cancer cells in vitro and increased therapeutic efficacy against human pancreatic tumor xenografts. [Mol Cancer Ther 2008;7(9):2845-54].     

Efficacy of GM-CSF-producing tumor vaccine after docetaxel chemotherapy in mice bearing established Lewis lung carcinoma

In this report, we evaluated the efficacy of a GM-CSF-producing tumor vaccine given before and after docetaxel in mice bearing established lung tumors. Mice bearing established 3LL tumors were treated with docetaxel and tumor vaccines transduced with either control or GM-CSF adenoviral vectors. Docetaxel (5-20 mg/kg) treatment alone had only a minimal effect on growth of established 3LL tumors in vivo, although docetaxel was cytotoxic to 3LL cells in vitro. When mice bearing established 3LL tumors were pretreated with docetaxel followed by vaccination with irradiated GM-CSF- transduced 3LL tumor cells, significant tumor regression and prolonged survival were observed compared with chemotherapy alone. Delaying docetaxel treatment until after tumor vaccination abrogated the vaccine's anti-tumor effects. Mice that survived treatment were able to resist a lethal rechallenge of 3LL tumor cells. Memory CTL specific for an epitope (MUT-1) derived from 3LL were detected in surviving mice. Docetaxel induced a mild lymphodepletion in mice, both CD4 and CD8 subsets were reduced in LN and spleens. Interestingly, docetaxel also diminished the number of memory CD8+ T cells (CD122+) and possible CD4+ CD25+ Foxp3+ natural Treg cells. Docetaxel treatment did not affect antigen-driven proliferation of naive T cells but significantly promoted survival of activated T cells. Thus, augmentation of vaccine induced antitumor immunity in docetaxel-treated mice primarily due to the enhanced survival of antigen-experienced T cells.     

Evidence for Conversion of 5-Fluorocytosine to 5-Fluorouracil in Humans: Possible Factor in 5-Fluorocytosine Clinical Toxicity

A gas chromatographic-mass spectrometric method for detecting 5-fluorouracil (5-FU) in serum at concentrations as low as 10 ng/ml was used to determine to what extent 5-FU was present in the serum of patients taking oral 5-fluorocytosine (5-FC). Preliminary studies in two patients and two healthy volunteers given an initial 2-g oral dose of 5-FC demonstrated sustained serum 5-FU levels (>100 ng/ml) during the 5 h after ingestion of drug. Pharmaceutical preparations of 5-FC used in these studies were shown to be insignificantly contaminated with 5-FU (<0.03%), suggesting in vivo conversion of 5-FC to 5-FU had occurred. Serum samples from seven patients with cryptococcal meningitis treated with amphotericin B and 5-FC were examined for 5-FU. Five of these patients had experienced hematological or other toxicity attributed to 5-FC at some time during the course of therapy. Of 41 serum samples, 20 were observed to have 5-FU levels greater than 1,000 ng/ml in the range observed with cancer chemotherapeutic doses of 5-FU known to be associated with hematological toxicity. It is concluded that conversion of 5-FC to 5-FU occurs in humans and furthermore that 5-FU may account for some of the toxicity observed with 5-FC.     

Targeted delivery of a suicide gene to human colorectal tumors by a conditionally replicating vaccinia virus

We have generated a thymidine kinase gene-deleted vaccinia virus (VV) (Copenhagen strain) that expressed the fusion suicide gene FCU1 derived from the yeast cytosine deaminase and uracil phosphoribosyltransferase genes. Intratumoral inoculation of this thymidine kinase gene-deleted VV encoding FCU1 (VV-FCU1) in the presence of systemically administered prodrug 5-fluorocytosine (5-FC) produced statistically significant reductions in the growth of subcutaneous human colon cancer in nude mice compared with thymidine kinase gene-deleted VV treatments or with control 5-fluorouracil alone. A limitation of prodrug therapies has often been the requirement for the direct injection of the virus into relatively large, accessible tumors. Here we demonstrate vector targeting of tumors growing subcutaneously following systemic administration of VV-FCU1. More importantly we also demonstrate that the systemic injection of VV-FCU1 in nude mice bearing orthotopic liver metastasis of a human colon cancer, with concomitant administration of 5-FC, leads to substantial tumor growth retardation. In conclusion, the insertion of the fusion FCU1 suicide gene potentiates the oncolytic efficiency of the thymidine kinase gene-deleted VV and represents a potentially efficient means for gene therapy of distant metastasis from colon and other cancers.     

Enzyme/prodrug therapy for head and neck cancer using a catalytically superior cytosine deaminase.

The use of cytosine deaminase (CD) in conjunction with 5-fluorocytosine (5-FC) has been studied for cancer gene therapy as a means of achieving tumor-specific generation of the toxic metabolite 5-fluorouracil (5-FU). Since 5-FC is frequently used as an antifungal agent, and because it has little or no efficacy as an antibacterial agent, we hypothesized that yeast CD (YCD) might be more efficient at utilizing 5-FC as a substrate and hence be a better choice for a CD/5-FC gene therapy strategy than the typically utilized bacterial CD (BCD). To that end Saccharomyces cerevisiae CD was cloned from yeast genomic DNA and expressed in vitro. Functional analysis of BCD and YCD expressed in COS-1 cells indicated that BCD and YCD both utilized cytosine with equal efficacy; however, 5-FC was an extremely poor substrate for BCD, with an apparent catalytic efficiency 280-fold lower than that observed for YCD. Retroviral infection of tumor cell lines in vitro indicated that the IC50 of 5-FC was 30-fold lower in YCD-infected cultures as compared with cultures infected with BCD retrovirus. In addition, when SCCVII murine squamous cell carcinoma cells were infected in vitro at low rates of infection (< or =10%) there was no significant cytotoxicity toward BCD-expressing cells while there was potent cytotoxicity to both YCD-expressing cells and "bystander cells" even at this low level of expression. Finally, stable BCD- or YCD-expressing SCCVII clones were developed and used in an orthotopic immune-competent model of head and neck cancer. Subsequent treatment with 5-FC followed by monitoring of tumor growth by noninvasive magnetic resonance imaging (MRI) and survival of animals indicated a growth delay during the course of 5-FC treatment for BCD-expressing tumors, which quickly regrew at the end of treatment. In contrast, YCD-expressing tumors exhibited not only a growth delay, which was of longer duration, but also in some cases frank tumor regression and complete cures occurred.     

High-dose, short-term, anti-inflammatory treatment with dexamethasone reduces growth and augments the effects of 5-fluorouracil on dimethyl-alpha-benzanthracene-induced mammary tumors in rats

OBJECTIVE: To evaluate the effects of dexamethasone (DXM) alone or in combination with 5-fluorouracil (5-FU) on dimethyl-alpha-benzanthracene (DMBA)-induced mammary tumors in rats. MATERIAL AND METHODS: Female Sprague-Dawley rats were divided into 4 groups receiving: 1) saline (controls), 2) DXM (3 mg/kg), 3) 5-FU (1.5 mg/kg) and 4) DXM and 5-FU combined. The drugs were given i.p. every day for 4 days. Interstitial fluid pressure (Pif) and tumor growth were determined in all tumors on days 1, 5 and 7 using the "wick-in-the needle" technique and by external size measurements, respectively. Vessel density and inflammatory cell infiltration of tumor tissue were analyzed by immunohistochemistry. RESULTS: DXM treatment significantly retarded tumor growth and reduced Pif. Treatment with a combination of DXM and 5-FU reduced tumor size significantly more than any of the agents alone (p<0.01-0.001). Enhanced uptake of 5-FU by DXM treatment was demonstrated by microdialysis. There were no differences in the density of CD31-positive vessels after DXM or 5-FU treatment, but inflammatory cell infiltration of tumor tissue was significantly reduced after DXM treatment. CONCLUSIONS: Our data suggest that DXM may be beneficial as an adjuvant to chemotherapy in the treatment of mammary cancer by increasing the uptake of 5-FU in the tumor.     

Human Neural Stem Cells Can Target and Deliver Therapeutic Genes to Breast Cancer Brain Metastases

The tumor-tropic properties of neural stem cells (NSCs) led to the development of a novel strategy for delivering therapeutic genes to tumors in the brain. To apply this strategy to the treatment of brain metastases, we made a human NSC line expressing cytosine deaminase (F3.CD), which converts 5-fluorocytosine (5-FC) into 5-fluorouracil, an anticancer agent. In vitro, the F3.CD cells significantly inhibited the growth of tumor cell lines in the presence of the prodrug 5-FC. In vivo, MDA-MB-435 human breast cancer cells were implanted into the brain of immune-deficient mouse stereotactically, and F3.CD cells were injected into the contralateral hemisphere followed by systemic 5-FC administration. The F3.CD cells migrated selectively into the brain metastases located in the opposite hemisphere and resulted in significantly reduced volumes. The F3.CD and 5-FC treatment also decreased both tumor volume and number of tumor mass significantly, when immune-deficient mouse had MDA-MB-435 cells injected into the internal carotid artery and F3.CD cells were transplanted into the contralateral brain hemisphere stereotactically. Taken together, brain transplantation of human NSCs, encoding the suicide enzyme CD, combined with systemic administration of the prodrug 5-FC, is an effective treatment regimen for brain metastases of tumors.     

自杀基因疗法结合HSP-PC瘤苗抗黑色素瘤研究

目的 :研究 5 -氟尿嘧啶 /胞嘧啶脱氨酶 (5FC/CD)基因疗法与热休克蛋白 -多肽复合物 (HSP -PC)瘤苗免疫疗法联合抗肿瘤效果。方法 :将携带CD基因的重组腺病毒注射到小鼠黑色素瘤体内 ,腹腔注射 5 -FC ,同时皮下接种HSP70 -PC。结果 :经联合治疗后 ,70 %荷瘤小鼠肿瘤体积缩小、消退 ,小鼠存活期延长 ,肿瘤组织明显坏死 ,炎症细胞、CD4+ 、及CD8+ T细胞浸润明显。结论 :5 -FC/CD基因疗法结合HSP -PC瘤苗免疫疗法抗小鼠黑色素瘤作用显著 ,具有临床应用前景。